FIG. 1 illustrates a simplified block diagram of a smart grid power supply arrangement 100 for an electronic control unit (ECU) 150, such as may form a part of an automotive system. In a smart grid power supply arrangement, multiple power supply lines are provided in parallel to supply power to components, such as the ECU 150 in FIG. 1.
The smart grid power supply arrangement 100 illustrated in FIG. 1 consists of two power supply lines, Vsup_1 102 and Vsup_2 104. The first power supply line Vsup_1 102 is coupled to a power supply VBat 105 via a first primary power switch 110. The second power supply line Vsup_2 is coupled to the power supply VBat 105 via a second primary power switch 120. The primary power switches 110, 120 consist of ‘smart’ power switches arranged to provide protection against, for example, over-current and over-voltage conditions on the respective power supply lines 102, 104.
The ECU 150 is coupled to the first power supply line Vsup_1 102 via a first secondary power switch 130, and to the second power supply line Vsup_2 104 via a second secondary power switch 140. The secondary power switches 130, 140 also consist of smart power switches arranged to provide protection to the ECU 150 against, for example, over-current and over-voltage conditions from the power supply lines 102, 104.
FIG. 2 illustrates the smart grid power supply arrangement 100 of FIG. 1 upon a short circuit to ground occurring on the second power supply line Vsup_2 104. When the second power supply line Vsup_2 104 is shorted to ground, a resulting over-current through the second primary power switch 120 will cause the second primary power switch protection circuitry to latch-off the second primary power switch 120, isolating the second power supply line Vsup_2 104 from the power supply VBat 105. As a result, the second power supply line Vsup_2 104 will be tied to ground, and have a voltage level of 0V. Consequently, the secondary power switches 130, 140 will end up being coupled in series between the first power supply line Vsup_1 102, having a voltage equal to the power supply VBat 105, and the second power supply line Vsup_2 104, having a voltage of 0V. In automotive applications and the like, the power supply VBat 105 may reach voltage levels in the region of, for example, 40V during a ‘load dump’. As a result, and as illustrated in FIG. 2, the first power supply line Vsup_1 102 may have a voltage level of 40V.
Thus, in the supply line short circuit scenario illustrated in FIG. 2, a 40V drop occurs across the secondary power switches 130, 140, with an initial low resistance path through the secondary power switches 130, 140 from the first power supply line Vsup_1 102 to the second power supply line Vsup_2 104.
A resulting high current flow through the first secondary power switch 130 will trigger the over-current protection functionality of the first secondary power switch 130, for example when the current flow exceeds a trip current of 50 A, causing the first secondary power switch 130 to be latched off.
A resulting high reverse voltage across the second secondary power switch 140 will trigger reverse voltage protection circuitry that will limit the reverse voltage across the second secondary power switch 140 (by allowing current to bypass the device when the reverse voltage exceeds a threshold, e.g. 22V).
As a result of the first secondary-power switch 130 being latched off, the ECU 150 is no longer coupled to an active power supply line, and thus no longer being supplied with power. Accordingly, although the original fault only occurred on one of the power supply lines (i.e. the short to ground on the second power supply line Vsup_2 104), the fault has resulted in the protection circuitry of the secondary power switches decoupling the ECU 150 from the fault-free power supply line, leaving the ECU without a power supply.